Global IFB means that any panel on the system will be interrupting the fold back audio going out on the IFB port.
It's a 4 step process...
1. You need to enable the "Global IFB" on the "Advanced Settings" for the IFB port and set the dim level or cutting level.
2. Add the IFB label to the panel or panels that need to talk to the IFB destination
3. Route the audio to the IFB, for this, go to "Local advanced"->"Forced listen" and add a crosspoint from the PGM (source) port to the IFB destination port.
4. Do an "Apply changes to frame"